ISLAMABAD, Pakistan (CNN) - U.S. Homeland Security Secretary Janet Napolitano, on a visit to Pakistan, discussed with Pakistani leaders the fight against terrorism, as well as how the two countries share information, she said Friday.

"The key concept is, you just can't start protecting the homeland at the borders of the United States," she said.

Napolitano has met with President Asif Ali Zardari and was to meet with the country's prime minister and interior minister.